This Information Applies To: Agilent OpenLab CDS
Issue
This article discusses different types of bracketing modes and how to set up a bracketed calibration in Data Analysis for OpenLab CDS 2.x
Background
Occasionally, the instrument conditions can change during a sequence of samples. The longer the runtime and the more samples in the sequence, the greater the likelihood of this happening. Hence, bracketing is used to compensate for the variation on instrument response with time.
With bracketed calibrations, the samples are bracketed by presample and postsample calibrations. The calibration standards between opening and closing brackets are processed first, and a calibration curve is calculated. This curve is then used to calculate the samples in this bracket.
For all bracketing modes except Custom, a Clear all calibration operation is automatically performed for all opening brackets. For the bracketing mode Custom, users can set the Run Type to Clear all calibration as required.
Bracketing is configured in the Injection List window. There are different bracketing modes:
Requirements
Steps to Follow
No bracketing. Samples and sets of calibration standards are processed in the order of acquisition. Amount and concentration of samples are computed with the calibration curve that is available at this point in time. Amount and concentration of calibration standards are computed with the calibration curve built from all standard injections present in the result set.
Figure 1 shows an example of None bracketing mode.
The compound in samples Batch001, Batch002, and Batch003 are quantified using the calibration points from calibration standard group 1 (blue box).
The compound in samples Batch004 and Batch005 are quantified using the calibration points from calibration standard group 1 (blue box) and group 2 (orange box).
Figure 1. None bracketing mode
Blue box is calibration standard group 1; Orange box is calibration standard group 2; Purple box is calibration standard group 3
The calibration curve is calculated with all calibration standards in the sequence, starting with the first one and finishing with the last one. All samples are reprocessed after the calibration curve has been calculated.
Figure 2 shows an example of Overall bracketing mode.
The compound in samples Batch001, Batch002, Batch003, Batch004, and Batch005 are quantified using the calibration curve from all three groups of calibration standard points (blue, orange, and purple boxes).
Figure 2. Overall bracketing mode
Blue box is calibration standard group 1; Orange box is calibration standard group 2; Purple box is calibration standard group 3
Users must have at least three groups of standards in their sequence. Standards from the group in the middle of the sequence are used in two calibration curves (with the preceding and with the following block).
Figure 3 shows an example of Overlap bracketing mode.
The compound in samples Batch001, Batch002, and Batch003 are quantified using the calibration curve from the calibration points of group 1 (blue box) and group 2 (orange box).
The compound in samples Batch004 and Batch005 are quantified using the calibration curve from the calibration points of group 2 (orange box) and group 3 (purple box).
Figure 3. Overlap bracketing mode
Blue box is calibration standard group 1; Orange box is calibration standard group 2; Purple box is calibration standard group 3
Users must have at least three sets of standards in their sequence, and at least two standards in the middle. The standards in the middle of the sequence are each used in one single bracket only. If there are more than two standards in the middle, they will be divided and allocated to the preceding and subsequent bracket. With uneven numbers of standards in the middle, the extra standard is allocated to the preceding bracket.
Figure 4 shows an example of Non overlap bracketing mode.
The compound in samples Batch001, Batch002, and Batch003 are quantified using the calibration curve from the calibration points of group 1 (blue box) and some of group 2 (orange box).
The compound in samples Batch004 and Batch005 are quantified using the calibration curve from some of the calibration points of group 2 (green box) and calibration points of group 3 (purple box).
Figure 4. Non-overlap bracketing mode
Blue box is calibration standard group 1; Orange box has two calibration standard points in group 2;
Green box has one calibration standard point in group 2; Purple box is calibration standard group 3
Create brackets as required. In the Run type column, users can choose for each calibration standard individually which calibration levels shall be cleared. If users do not choose any run type, a bracket will be averaged with its predecessor.
Figure 5 shows an example of Custom bracketing mode.
The compound in samples Batch001, Batch002, and Batch003 are quantified using the calibration curve from five calibration points (blue and orange boxes).
The compound in samples Batch004 and Batch005 are quantified using the calibration curve from all nine calibration points (blue, orange, and purple boxes).
With Clear all calibration in lines 10 and 16, the below example would correspond to an Overlap bracketing.
Figure 5. Custom bracketing mode
Blue box is calibration standard group 1; Orange box is calibration standard group 2; Purple box is calibration standard group 3
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